Interspecific competition between Microcystis aeruginosa and Chlamydomonas microsphaera stressed by tetracyclines

Abstract

The extensive tetracyclines in human and veterinary medicines cause contamination in the environment that could contribute to the antibiotic-resistant bacteria or the species competition in phytoplankton. In this study, Microcystis aeruginosa (bloom-forming cyanobacteria) and Chlamydomonas microsphaera (common green alga) were selected to test the effect of different concentrations of tetracyclines (tetracycline and oxytetracycline) in mono-culture and co-culture. The results showed that compared with mono-culture, the cell growth of C. microsphaera decreased signi cantly in co-culture treated with different concentrations of tetracycline and oxytetracycline. With the expose of 0.1, 2, 10 mg L -1 of tetracycline, the inhibition ratios of M. aeruginosa varied between 17.7% and 31.37% in co-culture compared to mono-culture, while the cell growth of M. aeruginosa was promoted treated with 0.1, 2, 7.25 mg L -1 of oxytetracycline in co-culture. However, the cell growth of C. microsphaera was signi cantly inhibited with all treatments in co-culture. With the treatment of tetracycline, the speci c growth rate of M. aeruginosa was 0.36 to 0.31 day -1 in mono-culture and co-culture, while that of C. microsphaera was ranged from 0.38 to 0.26 day -1 in mono-culture, and it decreased from 0.25 day -1 (0 mg L -1 ) to 0.08 day -1 (10 mg L -1 ) in co-culture. With the treatment of oxytetracycline, the speci c growth rate of M. aeruginosa was stimulated in co-culture while that of C. microsphaera showed an extremely signi cant inhibition in co-culture compared to mono-culture. Therefore, although M. aeruginosa outcompeted C. microsphaera in co-culture with the tetracyclines-free treatment, the competitive advantage of M. aeruginosa expanded upon addition of low or high concentrations of tetracyclines.